Potentiometer

ABSTRACT

This invention relates to a rotary, manually adjustable, compact potentiometer suitable for panel mounting and which requires a minimum of behind-panel space. The potentiometer comprises a central mounting assembly including a resistor supporting disc and a manually rotatable hollow knob rotatably mounted around the disc so as to form an enclosed resistor chamber. The central mounting assembly further comprising a flange spaced from the disc, an internal flange in the hollow knob trapped between the disc and the central mounting assembly flange, and an arcuate resistance element mounted in the resistor chamber on the disc. A resilient arm is driven by the knob in the resistor chamber and has a movable contact bearing on the resistance element. Electrical conductors extend through the central mounting assembly to the movable contact and resistance element.

United States Patent Hammond [451 Oct. 10, 1972 OTEN IOME ER Primary ExaminerLewis l-l. Myers Assistant Examiner-D. A. Tone [72] lnvemor' gi g ggg g iig Hammond Attorney-Frederick M. Arbuckle [73] Assignee: Bunker Ramo Corporation, Oak [57] ABSTRACT Brook This invention relates to a rotary, manually adjustable, [22] Filed: Nov. 15, 1971 compact potentiometer suitable for panel mounting and which requires a minimum of behind-panel space. Appl' l98804 The potentiometer comprises a central mounting assembly including a resistor supporting disc and a 52 use: ..338/163, 338/174 manually rotatable hollow knob rotatably mounted [51] Int. Cl. ..H0lc 5/02 around the disc so as to form an enclosed resistor 58 Field of Search ..338/163, 162, 174 Chamber The Central mounting assembly further I prising a flange spaced from the disc, an internal [56] References Cited flange in the hollow knob trapped between the disc and the central mounting assembly flange, and an ar- UNITED STATES PATENTS cuate resistance element mounted in the resistor chamber on the disc. A resilient arm is driven by the 3,044,033 7/1962 Mucher "338/163 knob in the resistor chamber and has a movable com 3,200,359 8/1965 Hulbert ..338/16 X tact bearing on the resistance element. Electrical con- 3,219,960 11/1965 Volkmann ..338/163 X l I l ductors extend through the central mounting assembly to the movable contact and resistance element.

8 Claims, 6 Drawing figures v PATENTED B I97? 3.. 6 97. 922

sum 1 or 2 BACKGROUND OF THE INVENTION 1 Field of the Invention This invention relates to a rotary, manually adjustable potentiometer which is compact, suitable for panel mounting, and requires a minimum of behind-panel space.

2. Description of the Prior Art Known manually adjustable potentiometers are not sufficiently compact for miniature components and require considerable behind-panel space. Further, the calibration indicia on small adjustable potentiometers are difficult to read because of their miniature size. There is an increasing demand for miniature components which occupy less behind-panel space and yet are convenient to use.

SUMMARY OF THE INVENTION A principal object of this invention is to provide a compact potentiometer suitable for panel mounting and which requires the minimum of behind-panel space. Another object is to provide a potentiometer which carries easily readable calibration indicia in spite of its miniature size.

According to one embodiment of the invention, the potentiometer comprises a central mounting assembly consisting of a central mounting post and a resistorsupporting disc forming a flange on the post, the post being adapted to fit through an aperture in a panel for mounting the disc in fixed relation to the panel. A manually rotatable hollow knob is rotatably mounted around the disc so as to form an enclosed resistor chamber. An arcuate resistance element is mounted in this chamber on the disc. A resilient arm carried by the knob in the resistor chamber has a movable contact bearing on the resistance element. Electrical conductors extend through the central mounting assembly to the movable contact and resistance element.

Another embodiment of the invention is a potentiometer which comprises a central mounting assembly including a resistor supporting disc and a manually rotatable hollow knob rotatably mounted around the disc so as to form an enclosed resistor chamber. The central mounting assembly further comprising a flange spaced from the disc, an internal flange in the hollow knob trapped between the disc and the central mounting assembly flange, and an acruate resistance element mounted in the resistor chamber on the disc. A resilient arm is driven by the knob in the resistor chamber and has a movable contact bearing on the resistance element. Electrical conductors extend through the central mounting assembly to the movable contact and resistance element.

In the preferred construction, the mounting assembly flange is clamped up against the panel, and the disc is on the front end of the post with the resistance element on the underside of the disc. A conventional brake assembly can be mounted between the mounting assembly flange and the internal flange of the knob.

In an alternative construction it is the disc which is clamped against the panel with the resistance element on the top side of the disc. The mounting assembly flange is on the front end of the post.

Another feature of the invention is that the top of the knob carries indicia, and the central mounting assembly also carries other indicia visible through the top of the knob. The two sets of indicia enable the setting of the potentiometer to read off. Thus, the top of the knob forms a top scale member, and the underlying top of the central mounting assembly forms a bottom scale member.

Preferably, a first one of the two scale members carries a radially inner main scale, and the second scale member carries an index mark against which the main scale is read. Either the first or second member additionally carries a radially expanded version of the main scale (with the same angular pitch between index marks), and the other member carries a vernier scale co-operating therewith.

The upper of these two vemier scales can be formed by windows through a relatively opaque ground, the lower scale comprising markings which contrast with the said ground, so that a single lower scale marking stands out where the vemier scales coincide.

Potentiometers have been made and tested with the above features with a knob 1 inch in diameter and less than one-half inch deep, enclosing the whole of the front of the panel structure, although the constructions illustrated hereinafter can be applied to potentiometers of any desired dimensions. Behind the panel is nothing more than a short threaded mounting post for receiving a fixing nut and washer. Such a potentiometer can be constructed with various types of resistance element such as wire-wound, metallized substrate, or conductive plastic to cover the whole range of full-scale values from ohms to l megohm, for example.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be described in more detail, by way of example, with reference to the drawings representing preferred embodiments of an improved potentiometer according to the present invention.

FIG. 1 is a perspective view of one potentiometer embodying the invention;

FIG. 2 is an axial section of the potentiometer with a wire-wound resistance element;

FIG. 3 is an axial section of the potentiometer with a metallized track resistance element:

FIG. 4 is a plan view of the potentiometer in FIG. 3 with a half section of the knob removed;

FIG. 5 is a perspective view of the preferred embodiment; and

FIG. 6 is an axial section of the potentiometer in FIG. 5.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The overall diameter of the potentiometers is about 1 inch, and externally the first embodiment, FIG. 1, comprises a knurled knob 10, including a transparent top 11, a threaded mounting post 12, a nut 13, and washer 14 on the post 12 for fixing the potentiometer to an apertured panel, and a disc 15 which forms a flange on the post 12.

Referring to FIGS. 2 and 3, the post 12 comprises a central core 16 with an integral enlarged boss 17 inside the knob 10. Lead-in wires 18, 19 and 20 extend through the boss 17 and core 16 which are moulded of insulating material. A sleeve 21 of such material pushed over the core 16 completes the insulation of the lead-in wires. A threaded metal bushing 22 is in turn pushed over the sleeve 21 to receive the nut 13.

An arcuate resistance element is mounted on top of the disc 15, extending over more than 300 for example. This element can be a wire-wound element 23 as shown in FIG. 2 or a metallized track 25 on a base 24, e.g. ceramic, as shown in FIG. 3. A conductive plastic can also be used. As shown in FIG. 4, for example, the two ends of the element are connected to the lead-in wires 19 and 20, e.g. via terminal pads 26.

The knob has a rebated skirt portion which mates over the disc 15, so that the knob forms a rotatable cap for this disc, enclosing a resistor chamber 40. The hol low knob has an internal flange or arcuate lip 28 which is trapped between the resistor-supporting disc and another disc or mounting assembly flange 29 fitted to the top of the boss 17. The knob is thus attached to the central mounting structure but can rotate thereon. The knob is biased resiliently against the disc 15 by a wave washer 30 between the lip 28 and disc 29.

The wave washer also forms part of a slip ring connection from the lead-in wire 18 to a movable contact 31 which rides on top of the resistance element as the knob 10 is rotated. Thus, a metal ring 32 on the underside of the disc 29 is soldered to the end 18a of the lead-in wire 18. A ring 33 of phosphor bronze, for example, is mounted on the upper surface of the lip 28. Integral with the ring 33 and attached thereto at diametrically opposite points is a resilient arm or semicircular yoke 34 which is given a downward selfbias. The movable contact 31 is provided at the center of the yoke 34 and the yoke springs this contact against the resistance element.

It will be apparent that assembly of the potentiometer requires the knob 10 minus the top 11 to be fitted over the central mounting assembly before at least one of the discs or flanges l5 and 29 is attached thereto. Subsequently, the top 11 can be fitted to the knob.

The transparent top 11 forms a top scale and the disc 29 forms a bottom scale, whereby the potentiometer is calibrated. One of the scales (it does not matter which) has a radially inner ring of indicia 35 (FIG. 4) which are read against a pointer 36 on the other scale. Full scale rotation can extend over 300 for example, with the indicia 35 at 30 intervals. The skirt 27 has a stop projection 27a which cooperates with a stop sector (not shown) on the disc 15 to prevent the knob being rotated clockwise beyond 300 or anticlockwise beyond 0.

At a radially outer position, the bottom and top scales 29 and 11 are provided with the two constituent scales of a vernier scale. The indicia of the top vernier scale are in the form of transparent radial slits 37 in an opaque band 38. The indicia of the bottom vernier scale are markings 39 which contrast with the band 38. Because of the well known vernier principle, only one of these markings will be visible at a time. As shown, it is the vernier marking 3. which shows, while the pointer 36 is just beyond 5. Therefore the potentiometer reads 53 ohms, assuming that the total resistance is 100 ohms.

One of the two vernier scales must have the same an gular pitch as the indicia 35, though it is not necessary for this vernier scale to be on the same member as the indicia 35. This first vernier scale can be called a radially expanded version of the main scale 35. The second vernier scale can either have a smaller pitch than the first vernier, specifically P (9/ 1 0) P where P and P are the first and second pitches in degrees, or the second scale can have the larger pitch, i.e. P l 1/ l 0) P It is preferable that whichever vernier scale is on the lower scale disc 29 shall have the larger of the two pitches, for the reason that the vernier indication will then rotate in the same direction as the knob 10 is rotated.

In the preferred embodiment, shown in FIG. 5, the knob 10, transparent top 11, mounting post 12, and the nut are again present. The post 12 has an integral mounting assembly flange 41 from which projects the tab 42 of a brake mechanism.

Referring to FIG. 6, the flange 41 is clamped against a panel by the nut 13 and washer 14, a stud 43 providing positive keying against rotation relative to the panel.

A resistor-supporting disc 44 is fixed on top of the enlarged boss 17, and an integral skirt 45 depends from the disc. The fixed scales are on the top surface of the disc 44 and cooperate with the moving scales on the transparent top 11. These scales can be as already described in relation to FIG. 3, and will not be described again in detail. However, one possible modification may be mentioned briefly. In FIG. 4 the whole of the main scale 35 is visible. If the main scale is on the disc 44 (or the flange 29 in FIG. 2), the annular band of the top 11 thereover can be opaque except for a window through which only that part of the scale which aligns with the pointer 36 is visible.

In the embodiment of FIG. 6, the resistance element is shown, purely by way of example, as a wirewound element 23 and is mounted on the underside of the disc 44, snugly inside the skirt 45. The knob 10 is rotatably mounted on the outer periphery of the skirt 45 and comprises and upper, outer shell 10a pressed on to an inner shell 10b. An internal flange 46, corresponding to the flange 28 of FIG. 2, is formed integrally with the inner shell 10b and closes the underside of the resistor chamber 40. The internal flange 46 is trapped between a shoulder 47 at the bottom of the boss 17 and an upstanding collar 48 round the inner periphery of the mounting assembly flange 41.

The flange 41 has an outer collar or upstanding rim 49 and a washer 50 nests within the annular channel between the collar 48 and rim 49. The washer 50 bears against another washer 5 5, which in turn bears against a resilient O-ring 51 housed in an annular groove in the underside of the knob flange 46. The washer 55 is fixed against rotation by lugs (not shown) which locate in recesses in the rim 49. The tab 42 is attached to the washer 50 and can rotate the washer between a free position, in which the knob can rotate, and a braked position in which the washer 55 jams against the O-rin g to lock the knob against rotation. To this end, the washer 50 is indented to form two upstanding pips 56 which are received in apertures 57 in the washer 55 when the washer 50 is the free position. When the washer 50 is rotated to the braked position, the pips 56 ride under the washer 55 and cam it upwardly to press against the O-ring 51. Such a brake mechanism is known per se, but it will be noted that, by putting the resistor supporting disc 44 at the top of the post 12 and the mounting assembly flange 41 against the panel on which the potentiometer is mounted, it is possible to retain a compact construction, with the track and contact structure inside the knob, and add thereto the brake facility.

A contact ring 33 resilient arm or yoke 34 and movable contact 31 are provided as in FIG. 2 but, in FIG. 6, they are mounted on the internal flange 46. The ring 33 is connected to the lead 18 by means of a slip ring 52 on the boss 17, and to which the lead 18 is connected. A C-clip or stirrup contact 53 slidably embraces the slip ring 52 and is attached to the ring 33.

In this embodiment, the sleeve 21 is hollow but closed at the bottom by a plug 54 through which the wires 18, 19 (not shown) and 20 pass. The boss 17 is integral with the sleeve 21. Obviously, these and many other details of construction, including the form of moving contact assembly, can be modified without departing from the scope of the invention.

What is claimed is:

l. A potentiometer comprising a central mounting assembly consisting of a central mounting post and a resistor-supporting disc forming a flange on the post, the post being adapted to fit through an aperture in a panel for mounting said disc in fixed relation to the panel, a manually rotatably hollow knob rotatably mounted around said disc so as to form an enclosed resistor chamber, an arcuate resistance element mounted in this chamber on said disc, a resilient arm driven by the knob in the resistor chamber and having a movable contact bearing on the resistance element, and electrical conductors extending through the central mounting assembly to the movable contact and resistance element.

2. A potentiometer comprising a central mounting assembly including: a resistor supporting disc; a manually rotatable hollow knob rotatably mounted around said disc so as to form an enclosed resistor chamber; the central mounting assembly further comprising a flange spaced from said disc, an internal flange in the hollow knob trapped between said disc and said central mounted assembly flange, an arcuate resistance element mounted in the resistor chamber on said disc, a resilient arm driven by the knob in the resistor chamber and having a movable contact bearing on the resistance element, and electrical conductors extending through the central mounting assembly to the movable contact and resistance element.

3. The potentiometer as claimed in claim 2, wherein the resistor-supporting disc is adapted to be mounted on a supporting panel with the mounting assembly flange in front of the said disc and inside the knob.

4. The potentiometer as claimed in claim 3, comprising a resilient washer disposed between the mounting assembly flange and said internal flange to urge the knob against the resistor-supporting disc.

5. The potentiometer as claimed in claim 2, wherein the mounting assembly flange is adapted to be mounted on a supporting panel with the resistor-supporting disc in front of said flange, inside the knob, and carrying the resistance element on its underside.

6. The potentiometer as claimed in claim 5, comprising a braking mechanism disposed between the mounting assembly flange and the said internal flange and operable to generate a wedging force on the internal flang to prevent rotation of the knob.

7. he potentiometer as claimed in claim 2, wherein the top of the knob carries indicia and the central mounting assembly carries other indicia visible through the top of the knob, whereby the setting of the potentiometer may be read off.

8. The potentiometer as claimed in claim 2, wherein said resilient arm comprises a yoke carried by said knob. 

1. A potentiometer comprising a central mounting assembly consisting of a central mounting post and a resistor-supporting disc forming a flange on the post, the post being adapted to fit through an aperture in a panel for mounting said disc in fixed relation to the panel, a manually rotatably hollow knob rotatably mounted around said disc so as to form an enclosed resistor chamber, an arcuate resistance element mounted in this chamber on said disc, a resilient arm driven by the knob iN the resistor chamber and having a movable contact bearing on the resistance element, and electrical conductors extending through the central mounting assembly to the movable contact and resistance element.
 2. A potentiometer comprising a central mounting assembly including: a resistor supporting disc; a manually rotatable hollow knob rotatably mounted around said disc so as to form an enclosed resistor chamber; the central mounting assembly further comprising a flange spaced from said disc, an internal flange in the hollow knob trapped between said disc and said central mounted assembly flange, an arcuate resistance element mounted in the resistor chamber on said disc, a resilient arm driven by the knob in the resistor chamber and having a movable contact bearing on the resistance element, and electrical conductors extending through the central mounting assembly to the movable contact and resistance element.
 3. The potentiometer as claimed in claim 2, wherein the resistor-supporting disc is adapted to be mounted on a supporting panel with the mounting assembly flange in front of the said disc and inside the knob.
 4. The potentiometer as claimed in claim 3, comprising a resilient washer disposed between the mounting assembly flange and said internal flange to urge the knob against the resistor-supporting disc.
 5. The potentiometer as claimed in claim 2, wherein the mounting assembly flange is adapted to be mounted on a supporting panel with the resistor-supporting disc in front of said flange, inside the knob, and carrying the resistance element on its underside.
 6. The potentiometer as claimed in claim 5, comprising a braking mechanism disposed between the mounting assembly flange and the said internal flange and operable to generate a wedging force on the internal flange to prevent rotation of the knob.
 7. The potentiometer as claimed in claim 2, wherein the top of the knob carries indicia and the central mounting assembly carries other indicia visible through the top of the knob, whereby the setting of the potentiometer may be read off.
 8. The potentiometer as claimed in claim 2, wherein said resilient arm comprises a yoke carried by said knob. 